1. Field of the Invention
The present invention relates to a data storage apparatus, such as a magnetic disk apparatus, loaded in a personal computer or the like.
2. Description of the Related Art
In a conventional magnetic recording apparatus incorporating a hard disk, loaded in an information equipment (e.g., a personal computer), data is protected by means of changing a file attribute (whether data can be read or written) or using a password, and a cartridge of the magnetic recording apparatus cannot be locked for the purpose of protection. Recently, however, a magnetic disk apparatus, in which a read/write operation can be prohibited by means of a lockable switch, is proposed (e.g., Jpn. Pat. Appln. KOKAI Publication No. 54-53509). Such a data storage apparatus with a lockable switch is applied to a desk-top apparatus but cannot be applied to a portable apparatus with a cartridge incorporating a memory medium.
In the conventional apparatus, to provide vibration resistance or impact resistance while a magnetic disk is being operated, a controllable frequency range of a magnetic head positioning control system is widened to increase the gain in a low frequency range. Alternatively, the magnetic head positioning controller is designed so that an open loop has a sufficient gain with respect to a frequency component corresponding to an external vibration applied to the magnetic disk or that a settling function has a sufficient suppression ratio with respect to a frequency component corresponding to an external vibration applied to the magnetic disk. In this case, servo information consisting of patterns repeated in a predetermined frequency on a part of the sector on a track which is called a servo sector is previously over the inner and outer peripheries of the magnetic desk. The servo information is read out by the magnetic head, so that the control for resisting impact is performed. For this reason, in the magnetic head positioning control system, data is sampled in a sampling period determined by the number of servo sectors and the rotating speed of the disk. Therefore, the controllable frequency range of the magnetic head positioning control system is limited by the sampling frequency. As a result, the magnetic disk apparatus cannot have a sufficient impact resistance. In order to provide a sufficient impact resistance, an acceleration sensor is arranged in a magnetic disk apparatus so that an impact applied to the magnetic disk apparatus during the operation of the disk apparatus is detected by the acceleration sensor, thereby prohibiting data from being written into a disk surface in accordance with the degree of the acceleration detected by the acceleration sensor. There is also a method of compensating an influence of impact or acceleration applied to the magnetic disk by feed-forward using an output from the acceleration sensor.
Recently, information equipment, i.e., a personal computer, has become more and more compact and light. In addition, a data storage apparatus itself, such as a magnetic disk apparatus, has become compact and highly integrated, and removable from a personal computer, a facsimile apparatus or a telephone set. Under the circumstances, the importance of security of recorded data has been increasing. To protect data, a password has been provided for recorded data, for example, a file of software. However, the password may easily be decoded by an unauthorized person or broken by a computer virus or the like.
The conventional method for obtaining a vibration resistance or impact resistance is to compensate an influence of vibration or impact in a magnetic disk operating time (while the magnetic disk apparatus is operating), and not in a magnetic disk nonoperating time (while the magnetic disk apparatus is not operating). Further, to increase the impact resistance in the magnetic disk non-operating time, mechanical measures have been taken: for example, to keep the magnetic head unloaded so as not to be brought into contact with the disk surface or to increase the latch force of a VCM (voice coil motor). Since the impact resistant performance of the magnetic disk apparatus in a disk non-operating time depends on mechanical factors as described above, it is necessary to increase mechanical impact resistance of the magnetic disk in order to increase the impact resistance performance of the magnetic disk apparatus in a disk non-operating time. However, it is very difficult and expensive to increase the impact resistance of the magnetic disk apparatus by means of mechanical factors.